Secondary Operator Research Articles

Sequences involved in growth-phase-dependent expression and glucose repression of a Streptomyces -amylase gene

In glycerol-grown, but not in glucose-grown cultures, expression in Streptomyces lividans TK24 of the cloned alpha-amylase gene (aml) of Streptomyces limosus is switched on toward the end of exponential growth. During this period, aml expression is further inducible by maltotriose. We showed that a 378 bp fragment, extending from position -204 through to +174 (relative to the transcriptional start site), included cis-acting sequences involved in aml regulation. When this fragment was present on a multicopy plasmid, the growth-phase-dependent aml expression conferred by a DNA fragment cloned on a compatible low-copy-number plasmid was greatly enhanced, as if negative regulators were being titrated. A study of the regulation of aml expression in variants with deletions in the aml promoter region indicated that a direct repeat (DR) between positions -124 and -106 (relative to the transcriptional start site) and an inverted repeat (IR) between positions +9 and +24 were good candidates for secondary and primary operator sites, respectively. Deletion of a 29 bp fragment containing the IR rendered aml expression partly growth-phase-independent, resistant to glucose repression, and insensitive to maltotriose induction.

Influence of sequence and distance between two operators on interaction with the lac repressor.

The influence of additional operator or pseudooperator sequences on the lactose repressor-operator interaction has been investigated. Results of kinetic and equilibrium binding measurements suggest an important in vivo role for the Z-gene pseudooperator in repressor-operator binding; the formation of a ternary, looped complex is indicated by the influence of secondary operator sites on binding parameters. Although the binding affinity of the Z-gene pseudooperator [Oz] is only approximately 1/30 that observed for the primary operator [O], the binding affinity to DNA containing both Oz and O is significantly higher than either sequence alone or the sum of the two. This synergistic effect is enhanced further by replacing the pseudooperator sequence [Oz] with the primary operator sequence and results in an even stronger ternary complex in plasmids with duplicate primary sites. The distance between the center of the two primary operators affects the formation of a ternary complex in the linear DNA molecules. Decreased dissociation rate constants were observed with spacing of operator-like sequences between 300 and 500 base pairs (bp). Minimal influence of the second operator on repressor binding is observed when the operators are separated by approximately 4000 or approximately 100 bp. The significant influence of distance on kinetic and equilibrium parameters was demonstrated by measurements on plasmid pRW1511 [Oi-O-PL-Oz] cleaved with restriction enzymes either in the polylinker region to place Oi-O and Oz on opposite ends of the linear plasmid or outside this region to maintain the sites within 500 bp. These results are consistent with the formation of operator-repressor-pseudooperator ternary complex to generate a looped DNA structure.

Secondary differential operators

Let Ч be an arbitrary sustem of partial (non-linear differential equations. Higher infinitesimal sysmmetries of Ч may be interpreted as vector fields on the «manifoldå Sol Ч of all local solution of this system. The paper deals with construction of differential operators of arbitrary orders on Sol Ч. These approaches to construction of the theory of these operators, geometric and functional are presented, and their equivalence is proved when Ч is the trivial equation. Coincidence of «extrinsicå and «intrinsicå geometric secondary operator is proved for an arbitrary system Ч. It is shown that each geometric secondary operator may be approximated by a sum of compositions of evolution differentiations with any possible accuracy, a description of geometric secondary operators in local coordinates is algo given. These results are obtained by studying the geometry of finite jets and infinitely prolonged equations.

Binding of lac repressor to the secondary lac operator in Escherichia coli

In the lac operon, the existence of a secondary repressor binding site, inside Z gene, had been inferred from in vitro binding studies (Reznikoff et al., 1974; Gilbert et al., 1975). A series of deletions have been constructed from a lac transducing lambda bacteriophage. Some of those deleted bacteriophages have still the property of derepressing a chromosomal lac operon, even though they do not contain any more the lac operator. This phenomenon is an indication that the secondary repressor binding site is also active in vivo.

On the Theory of Obstructions

N. E. Steenrod has solved1 the homotopy classification problem for maps K -+ S', where n > 2 and K is an (n + 1)-dimensional polyhedron. His solution is stated in terms of separation cochains and depends on a certain theorem concerning obstructions (cf. (6.1) below). The latter, likewise the homotopy classification theorem, has been extended by M. M\. Postnikov and also, for n = 2, by Hassler Whitney to the case of maps in an (n 1)-connected space X, which is arbitrary except that 7r1(X) is finitely generated.2 The main purpose of this note is to show how the theory of composite chain systems ([11], ?4) and the secondary boundary operator can be used in proving the theorems of Postnikov and Whitney. Our conditions are more restrictive than theirs, since we eventually confine ourselves to finite complexes. This is because our definitions of the squaring operations (?5 below) do not apply to infinite complexes. However the same theorems can be proved, by an elaboration of our methods, for maps of a finite complex in an arbitrary (n 1)-connected space. This was done in an earlier draft. But the simplification due to the relation (5.9) below, for which the image space is also required to be a finite complex, seems to justify the loss of generality. In revising the first draft I have been greatly helped by a series of discussions with Steenrod, who suggested the use of the difference homomorphism and the relation (5.9).

The Secondary Boundary Operator

The Secondary Boundary Operator